American Cancer Society Study Finds the Most Common Type of Lung Cancer in the US is on the Rise

American Cancer Society
Thursday, 29 June 2000

The increase in the incidence of adenocarcinoma of the lung, the most common type of lung cancer in the US, is associated more with changes in smoking behavior and cigarette design than with diagnostic advances, according to a new study from the American Cancer Society. The findings are reported in the November 5, 1997, issue of the Journal of the National Cancer Institute.

In the late 1950s and 1960s, squamous cell carcinoma was about three times as common as adenocarcinoma. Although squamous cell carcinoma was clearly linked to smoking, the relationship between tobacco smoke and adenocarcinoma of the lung was described by researchers as "slight, if any." But by the late 1980s, adenocarcinoma had become the most commonly diagnosed lung cancer in the US.

The present study was undertaken to determine whether the increase was attributable to advances in diagnostic technology (i.e., increased ability to perform biopsies in smaller airways), or to changes in cigarette design (the adoption of filtertip, lower tar and nicotine products) and concomitant changes in smoking practices. Lead author Michael J. Thun, MD, director of analytic epidemiology for the American Cancer Society, and colleagues from the Society, Emory University and the Connecticut Tumor Registry, examined data from the Connecticut Tumor Registry for 1959 through 1991 and compared the first two years of follow-up in Cancer Prevention Study I (CPS-I, initiated by the American Cancer Society in 1959) with Cancer Prevention Study II (CPS-II, initiated by the Society in 1982).

The researchers found that the incidence of adenocarcinoma increased nearly 17-fold in women and nearly 10-fold in men from 1959 through 1991. According to Dr. Thun, the increases followed a clear birth cohort pattern, paralleling gender and generational changes in smoking more than diagnostic advances. Cigarette smoking became more strongly associated with death from adenocarcinoma of the lung in CPS-II compared with CPS-I, with relative risks of 19.0 for men and 8.1 for women in CPS-II, and 4.6 for men and 1.5 for women in CPS-I.

"The American Cancer Society studies clearly implicate smoking as the major cause of adenocarcinoma, as well as of other lung cancers," notes Dr. Thun. "The death rates from adenocarcinoma remained low and essentially unchanged from CPS-I to CPS-II in lifelong nonsmokers, but they increased markedly in smokers. The apparent increase in relative risk between cigarette smoking and death from adenocarcinoma in CPS-II relative to CPS-I is consistent with a trend toward higher relative risk estimates observed in other epidemiologic studies over time," says Dr. Thun.

"The findings are important because they link the rise in adenocarcinoma among smokers and people exposed to secondhand smoke to changes in tobacco smoke exposure rather than other factors," says Dr. Thun. "They also illustrate how past attempts to design less hazardous cigarettes have largely not been successful."

While most squamous cell carcinomas develop in the large airways, adenocarcinomas usually develop in smaller branches toward the outer edges of the lungs. These two types of cancers are distinguished by their appearance under the microscope. Squamous cell carcinomas are formed by flat cells that resemble skin cells. Adenocarcinomas are composed of tall, cylinder-shaped glandular cells that often produce mucus.

Before the 1950s, smoke from cigarettes was to irritating to be inhaled deeply, and most of the carcinogens were deposited in the larger airways closer to the throat. Since then, the popularity of filters and new tobacco blends allows smokers to inhale more deeply. This smoking pattern deposits carcinogens in the small airways deeper in the lungs - the areas where adenocarcinomas form.

Co-authors of the study include Eugenia E. Calle, Clark W. Heath, Jr., and Cathy A. Lally, American Cancer Society; John T. Flannery, Connecticut Tumor Registry, State Department of Health; and W. Dana Flanders, Emory University.

The American Cancer Society is the nationwide, community-based, voluntary health organization dedicated to eliminating cancer as a major health problem by preventing cancer, saving lives and diminishing suffering from cancer, through research, education, advocacy, and service. For more information about cancer or the American Cancer Society and its programs, contact your local American Cancer Society or call 1-800-ACS-2345.

For more information, or to contact American Cancer Society, see their website at: www.cancer.org